I. Field of the Invention
The invention relates to asphalt compositions and to a process for the improvement of their properties. The invention further relates to modified asphalt compositions useful in a variety of applications, particularly paving asphalts, and to construction methods utilizing such compositions.
II. Description of the Prior Art
Asphalt based materials are used extensively in a wide variety of applications. For example, asphaltic material is widely employed as a primary ingredient in coating compositions for structures, in sealants, and in waterproofing agents. Asphalt compositions have been used in paving mixtures with considerable advantage for many years. Many manufactured roofing materials, such as roofing shingles, impregnated felts, tars, mastics, and cements are also based on asphalt and compositions thereof.
U.S. Pat. No. 3,930,988 to Johnson (Phillips) teaches the process for treating used motor oils for reduction in ash content and metals. Further treatment by filtration through absorbents and then hydrotreating renders an oil product suitable for reuse in lubricating stocks. This patent provides a process for preparing lubricating materials which may be suitable for use in the present invention but does not teach the significance of using lubricating stocks with asphalt for improvement in low temperature performance properties.
U.S. Pat. No. 4,250,021 to Salusinszky teaches a process for removing metals and water from used lubricating oils rendering a product suitable for refinery feedstocks, fuel oil, or as blend stock for other hydrocarbon products or as rerefining feedstock. The claims of the reference deal strictly with the process of treating used oil materials and the ingredients used therein. No mention is made relative to the present invention which finds particular advantage in using a predominately paraffinic lube stock as a diluent/plasticizer for enhancing the low temperature properties of asphalt paving compositions.
U.S. Pat. No. 4,381,992 to Wood et al. (Phillips) teaches the process for purification of used oil by removal of the ash forming components and then subjecting the material to vacuum fractionation. The patent discusses that such fractionation renders a bottoms material too heavy for use as a lubricating oil, but useful as a gear oil or as an asphalt additive. No further mention of usefulness of the bottoms material is made. The claims of the invention deal only with the purification of used oil processes, a method for fractionating the same and in no form discuss the novel findings of our invention.
U.S. Pat. No. 5,098,556 to Go et al. (Lyondell) teaches the purification of white oils to remove color producing bodies detrimental to the acid treating process. The invention teaches the process for passing white oils through acid treated clay filtration to remove RCS (readily carbonizable substances) which render the oils undesirable for use. It does not teach the use of oils for improving low temperature performance of paving grade asphalts. The oils produced by this invention could be used in the present invention as alternatives to the specified hydrofinished neutral oils. However, their cost from the purification process would render them unattractive for use in asphalt.
U.S. Pat. No. 3,455,716 to Loring et al. (Sinclair) teaches the production of film forming coating compositions providing corrosion inhibiting properties. No mention is made of their usefulness in asphalt paving compositions for improvement of low temperature performance.
U.S. Pat. No. 2,970,099 to Illman (Shell) teaches the alkylation of asphaltenes for the improvement of weathering, viscosity-temperature slope, and sweating tendencies of asphalt compositions. The invention further comprises oxidation or air blowing of the asphalts in conjunction with alkylation. Further it teaches the use of 25 to 75 parts by weight of a mineral lubricating oil, well outside the range of usage within our invention, with the alkylated asphaltenes for use as roofing asphalts. The present invention does not require alkylation, however, the use of asphalts produced by the process of this reference may be used within our invention as the base asphalt. Illman does not teach the use of neutral oils for improvement of low temperature properties of paving asphalts or the blowing of mineral lubricating oil-containing asphalt compositions for such purpose.
U.S. Pat. No. 2,947,697 to Vierk et al. (Sinclair) teaches the production of protective wire rope lubricants comprising oil, polyethylene and oxidized asphalt. It does not teach the findings of the present invention for paving asphalts.
U.S. Pat. No. 2,870,080 to Illman et al. (Shell) teaches the production of an oil asphalt plastisol comprising a continuous oil phase in which a pulverized asphalt is suspended. Said composition of this invention is not homogeneous nor continuous until heated and fused at temperatures above the softening point of the asphalt component. Said asphalts in this invention will have 0-5 penetration and softening points of 82-116.degree. C. (180-240.degree. F.). The reference teaches the production of said asphalts by severely high steam distillation or solvent precipitation and said asphalts then being ground to a fine particle size and suspended in an oil carrier to form a plastisol with lower processing and handling viscosities until fused back into a continuous phase. The invention does not teach the novel findings of our present invention for producing low temperature grades of Superpave asphalts.
U.S. Pat. No. 5,397,459 to Butler (Exxon) teaches the low severity hydrotreating of used lube stocks which contain only low levels of additives such as industrial circulating oils. Such oils are required in low severity lubricating applications to produce lubricating base stock oils. This invention could produce oils suitable for use in our present invention. It does not teach the use of said oils with asphalts for low temperature performance improvements.
III. Problems Presented by Prior Art
Regardless of the particular manner of formation or application of the particular asphalt mixture, durability is an important matter in the case of most asphaltic materials. For instance, in the case of a paving asphalt composition, durability of the road surface is a primary concern. The degree and rate of hardening of the paving asphalt composition or cement during application and while in service (so-called "age hardening"), caused by an increase in viscosity of the asphalt mixture and gradual loss of flexibility, are factors affecting the durability of an applied surface. At least one worker in the art (i.e., Januschke, Industrial Engineering Chemistry Product Research and Development, Vol. 10, 1971, 209-213) has concluded that the reaction of the asphalt composition with atmospheric oxygen is the principal cause of asphalt hardening in pavement. Accordingly, the retardation of age hardening has been the object of extensive study.
Conventional refined asphalts have been found through the implementation of the Strategic Highway Research Program (SHRP) (now Superpave binder implementation) to be incapable of meeting requirements for resistance to low temperature thermal cracking in certain climatic areas or conditions. Modification using various types of modifiers such as plastomers, elastomers, chemical gellants, and chemical modifiers does not fully satisfy the improvement required in both high temperature rutting resistance and low temperature cracking resistance.
Conventional practice has been to add softer asphaltic compounds or aromatic oils or other additives to soften or plasticize the asphalt composition. In order to reach acceptable low temperature properties, excessive amounts of soft asphaltic materials or fluxes must be added. In addition, aromatic oils are normally required in such amounts that when used in combination with polymers (through the action of the increased aromaticity from the oil) cause the amount of polymer required to reach the desired level of rutting resistance to become excessive from a cost standpoint, eliminating the composition from use as a paving composition.
As a result of the 1987 Intermodal Surface Transportation Efficiency Act (ISTEA), a $150 million research study was commissioned in which $50 million was spent towards asphalt research for improving asphalt pavements. As a product of that research which was concluded in 1992, the Strategic Highway Research Program (SHRP) produced what is now known as the Superpave Performance Graded Binder Specification in which asphaltic binders are graded or characterized according to their relative performance in resistance to rutting, shoving or deformation at high temperatures, fatigue at intermediate temperatures, and thermal cracking resistance at low temperatures. Asphalts which normally would be graded either under the penetration or viscosity specifications will now be graded as PG or Performance Graded binders. As such, their designation will be representative of their resistance at both high and low temperature, indicating their useful temperature range as a PG AA-BB where AA=high temperature resistance in degrees Celsius and BB is low temperature cracking resistance in minus degrees Celsius, i.e., PG 64-22 would prevent rutting up to 64.degree. C. (147.degree. F.) and low temperature cracking to a minus 22.degree. C. (-7.6.degree. F.). Areas of high loading or slow or standing traffic as well as areas where temperature extremes can be experienced in excess of 86.degree. C. (155.degree. F.) between high and low temperature levels will require the use of modifiers to obtain the increased useful temperature range. As a result, it has been common to add or start with softer asphalts to reach low temperature properties while adding modifiers such as polymers to achieve high temperature rutting resistance. The use of aromatic oils has been included to also give low temperature properties. As such, extensive levels of polymer addition are required to regain high temperature properties, especially when using aromatic oils as their use tends to solvate the polymer to a higher degree and thus require a higher level of polymer to be used to obtain the desired property.
U.S. patent application Ser. No. 08/697,385, filed Aug. 23, 1996 (docket number 6505AUS), discloses the addition of mineral lubricating oil to an asphalt component, including oxidized asphalt component, for the purpose of improving the properties of the resulting blend. However, the application does not disclose oxidizing the blend of asphalt: component and mineral lubricating oil.
Notwithstanding the considerable previous efforts expended to provide asphalt compositions having improved low temperature cracking resistance, and to provide a method of improving asphalt durability, there has remained a continuing need, particularly with paving asphalts, for improved compositions and methods. The invention addresses this need.